Magnetic switching element driver circuits



Feb. 19, 1957 D. H. LEE

MAGNETIC SWITCHING ELEMENT DRIVER CIRCUITS Filed April 16, 1954' FIG. IA

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United States Patent MAGNETIC SWITCHING ELEMENT DRIVER CIRCUITS Donald H. Lee, Philadelphia, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application April 16, 1954, Serial No. 423,628

18 Claims. (Cl. 307-458) This invention relates to magnetic switching elements and more particularly to means for effecting switching of the storage state of a plurality of elements in response to synchronized triggering potentials.

Magnetic switching elements have been extensively used in shift registers of the prior art as indicated by such articles as that entitled An Electronic Digital Computer, published in Electronic Engineering, December 1950, by A. D. Booth. The magnetic switching elements of these registers have magnetic cores exhibiting a substantially Accordingly, the elements tend to remain in one or the other permanent magnetic remanence condition after being driven into magnetic saturation by signals presented at a transformer winding about the element. In order to drive the magnetic elements into saturation, considerable driving current is required, and the current waveform must be rigidly controlled to prevent storage of spurious signals. Difficulty is also encountered in isolating current driving sources from transient conditions occurring in the transformer windings about the magnetic element due to changes in the storage state of the elements.

For example, the loading upon the current source changes considerably between an unswitched and switched condition of the element, since the element is saturated when switched and therefore presents very small inductance as compared with the unsaturated inductance. In addition, when the cores have their magnetic state disturbed by means of inputsignals at transformer windings about the cores, noise signals are generated in the advancing windings coupled with the driver circuits. Whenever the element is changed from an unswitched condition to a switched condition, the potential developed in the advance windings becomes large enough to limit the utility of those advance circuits in which more than a few elements are connected.

Although gaseous driving circuits were otherwise desirable, because of the high current pulses of good waveshape which could be obtained from them, they could not be successfully used in the prior art to drive magnetic switching element circuits because of the aforementioned transient and noise conditions inherent with the magnetic switching elements, which prevented that precisely controlled error-free operation of the elements necessary to attain in order to utilize the switching elements in highspeed computer circuit operation, or the like.

It is, accordingly, a general object of the invention to provide improved and reliable current driving circuits for magnetic switching elements.

A further object of the invention is to aiford gaseous tube switching element driving circuits.

The invention therefore provides a series current driving circuit for magnetic switching elements comprising a gaseous tube, which may be triggered from a suitable source, a pulse forming storage network, and a series of the magnetic switching element driving windings. Separate charging and discharging circuits are provided for thestorage network, with the switching element windings 2,782,324 Patented Feb. 19, 1957 being coupled only in the, discharging circuit in order to prevent the switching elements from being partially switched during charging of the storage network. In addition, the invention provides inhibiting means for preventing spurious triggering of the gas tube driving circuit in response to noise pulses excited in the switching element driving circuit transformer windings. Thus, it becomes advantageous to use gaseous tube driving circuits in combination with magnetic switching elements in accordance with the teachings of the present invention.

Further features and objects of the invention will be found throughout the following description and accompanying drawings, in which:

Fig. 1a is a schematic diagram of a magnetic shift register with accompanying block diagrams of gaseous tube driver circuits afforded by the invention;

Fig. lb is a hysteresis loop diagram illustrating the manner of operation of the magnetic switching elements used in connection with the invention;

Fig. 2 is a schematic circuit diagram of a gaseous tube magnetic switching element driver system constructed in accordance with the teachings of the invention; and

Fig. 3 is a schematic circuit diagram of a further embodiment of the invention.

Like reference characters are used to designate similar features throughout the drawings in order to facilitate comparison of the several views.

More specific reference may be made to Fig. la in order to understand the operation of gaseous tube driving circuits afforded by the invention in connection with the conventional magnetic shift register circuit 10. In this type of register circuit alternately occurring shift a and shift 3 pulses are provided for shifting stored information respectively out of magnetic elements A and B of the register, while at the same time switching the storage state of the elements to a reset condition for receiving further storage information from the foregoing elements. Shifting windings 13 and 14 are provided on the respective elements A and B, through which driving current pulses flow. Each of the magnetic shift elements is provided with a core material 16 having a substantially rectangular hysteresis characteristic illustrated by the typical curve of Fig. 1b. This material has the property of remaining in one of two permanent magnetic remanence conditions referred to as 0 or 1. The legends associated with the transformer windings indicate that for input signals the current is passed through the appropriate winding in such a direction and magnitude that either a 0 or 1 is stored in the core. Likewise the legend connected with an output winding indicates that an output signal is provided when the element is switched from the opposite remanence condition to that shown in the legend. This is accomplished by the rectifier in the output coupling circuit, which permits current to flow only in one direction, even though potentials are induced in the output windings whenever the remanence state is altered in either sense.

Referring again to the hysteresis curve of Fig. 1b, current driving pulse Waveforms 18 and 23 for providing enough magnetizing force H to set the cores in respective states 0 and 1 are shown. Thus, the elements are ordinarily reset in the condition 0 by a current driving pulse 18 no matter what the previous storage condition is. If the core is initially in a 1 remanence condition, the reset pulse 18 will cause the hysteresis characteristic to traverse the side 20 and go into magnetic saturation at point 21, from which it will return to the magnetic remanence condition 0. Should the information have been in the 0 condition already, the hysteresis curve would be traversed from O to point 21 and back again. Thus, with the same change in magnetizing force there is proportionately a very large or small change in the flux density B, depending upon the previous storage state. A large change in flux density signifies a high inductance, so that the core appears to have a high inductance during the switching operation from one state to another, therefore providing close coupling between the shifting winding 13 and the output winding. After the core has been reset to a condition, a read-in signal 23 may be provided for switching the core to a 1 condition. Thereafter the 1 may be transferred out of the element by means of the shift or reset driving pulse 18. In this general manner information is read into and passed along the shift register 10 by means of alternate driving pulses at shift windings 13 and 14 of elements A and B.

High current driving pulses are derived from voltage triggering pulses Eat and E3 in accordance with the invention by means of gaseous tube driving circuits 25 and 26. The gaseous tubes may be either grid controlled thyratrons or triggered cold cathode tubes. Good waveform control is attained with the triggered gaseous tubes when supplied with a DC. anode supply source, since the signal on the trigger electrode loses control after the discharge is initiated, with a resulting high current flow highly desirable for switching magnetic storage elements.

Note that a voltage is induced in each transformer winding during the switching operation, and therefore the shift windings 13 and 14 will be subject to periodical noise pulses of opposite potential to that afforded during the shift operation whenever information is stored in their associated cores by a read-in pulse 23. This means that the switching element load circuit must be disassociated from the gaseous tube driver input circuit, since the gaseous tubes may be triggered by the change of potential in the shift windings. Should a pulse forming network or delay line 28 be used in connection with the gaseous tube driver 26 to form a desirable square wave driving waveform, it is also necessary to provide separate charge and discharge paths for the delay line. Otherwise current flow through the driver circuit during the charging cycle would tend to disturb the remanence condition, as the current flow changes direction and tends to read information of opposite polarity into the element.

Details of operation are described in connection with the schematic diagram of Fig. 2, wherein the shift register 10 operates in the conventional manner of that shown in Fig. 1. Consider first the shift pulse actuation of elements B of shift registers which are triggered by the input voltage E1 at the shift [3 input terminals. The gaseous thyratron tube 26 has its control grid returned to -l volts cult-off potential, and is thereby triggered by a positive shift {3 command. Assuming the tube 26 to be in an extinguished state, the lumped parameter relay line 28 is charged through resistor 31 from the +250 volt supply to 100 v. established by means of the series resistor 30 and diode 32. The delay line stores a fixed increment of energy which may be quickly discharged in the form of a current pulse of substantially square waveform through the thyratron 26, because resistor 31 (with diode 32 blocking current flow) permits only a small current flow from the 250 volt supply to oppose such discharge current. Therefore, the delay line 28' discharges substantially through the core load circuit windings 14 when the thyratron is caused to fire. In this manner desirable high current driving pulses are provided for shifting information from the B cores into the succeeding A cores of the shift register.

In order to successfully drive the shifting circuit with gaseous tube drivers, several precautions are necessary. It is noted that current should pass through windings 14 only in the direction designated by the arrows in order to provide proper shifting action in the shift register. Should the current flow in an opposite direction, it would tend to disturb stored information and make the register inoperative due to noise generated thereby. For this reason it is necessary that the gaseous tube, core load and delay line be connected in a series delay line discharge circuit, and that a separate branch comprising resistor 33 (and excluding windings14) be provided for the charging current path of the delay line. Accordingly, the windings 14 are placed in the plate load circuit of the thyratron 26. This is not always convenient however, since the windings 14 must therefore be insulated for high voltage operation. When the cores, which are generally of toroidal configuration, are made smaller, it is diificult to afford windings with the proper insulation because of the limited space and the tendency of insulation to crack as the radius of winding curvature becomes smaller.

An alternative load connection is therefore provided for the cold cathode driver 25. This driver circuit supplies the A cores with shift a pulses in the same general manner hereinbefore described. However, the shift windings 13 are in the cathode circuit of the cold cathode gaseous tube 2.5, and therefore need not require high voltage insulation. But, since the windings are thus in the input circuit of the tube, and current flows through the shift windings 13 in the direction of the arrows when the delay line is discharged, a potential of opposite polarity is induced in the shift windings when a 1" signal is shifted into the A elements. Accordingly, the windings in the cathode to ground path of the discharge tube constitute a source of input potential of the necessary polarity for triggering the discharge tube at a time other than that of the arrival of a shift a pulse. Accordingly, the cathode loaded gaseous tube driver is subject to false triggering by noise impulses unless inhibiting means are provided for preventing undesirable discharge of the tube 25 due to the potentials excited in the shift windings 13 when the A cores are switched to 1 states by incoming signal pulses. For this reason an inhibiting capacitor 36 is provided between the cathode and triggering electrodes of the cathode loaded gaseous tube. This capacitor maintains the triggering electrode and cathode at the same A.-C. potential for noise impulses excited in the shift windings 13. Accordingly, operation may be effected with gaseous tubes having switched element loads connected in the cathode circuit in this embodiment of the invention. The noise impulses have a more pronounced effect as more information is stored in the register, and as more cores are placed in series in the discharge path. Accordingly, operation with more than a few cores is not possible without the described inhibiting circuit of the present invention.

Alternatively the load circuit may be placed in the delay line ground return as shown in Fig. 3. In this event, however, both charging and discharging current of the delay line would tend to fiow through the inductive shift windings without necessary precautions for separating the charging and discharging paths, as is done in the aforedescribed embodiments by having a charging path independent of the shift windings. A compensation network is therefore necessary. Thus, a diode 39 placed in series with the shift winding load of register 10 permits current to flow only in the desired direction during discharge of the delay line. Charge current for the delay line 28' conversely flows through a shunt resistive charging path 41, because of the high back impedance of diode 39.

When the gaseous tube is triggered by a magnetic element 40, a current limiting resistor 42 need be provided to prevent noise in the magnetic element due to the grid current.

In the cold cathode driver embodiment of Fig. 2 the delay line 28" is a distributed parameter line, and the diode circuit is not provided in the charging path. Without the diode, the repetition frequency of the shift pulses may be limited by the longer necessary charging time of the delay line. The diode 32 when provided operates as a clamp after the delay line charges to volts from the 250 volt supply'to assure a constant charge in a small portion of the normal exponential charge time of the line, so that the system is not pulse repetition frequency sensitive. Otherwise when the delay line is triggered before the full charging period, lower amplitude output pulses would be provided. The cold cathode gaseous tube 25 also operates differently from the thyratron 26' in that it has considerable internal impedance. The lumped parameter delay line 28 of the thyratron 26 is terminated in an impedance comprising essentially only the core load circuit and resistor 33, since the impedance of thyratron 26 is small. In general, the core load circuit is made to have a maximum impedance, with each core being switched, which is lower than that of the characteristic impedance of the delay line. This affords the most desirable operation in presence of the changes in loading imposed upon the circuit when fewer bits of information are shifted along the register. The impedance of cold cathode tube 25' however, substantially contributes to the terminating impedance of the delay line 28". Therefore, the overall impedance of the tube and the shift on winding 13 should be less than the characteristic impedance of the delay line 28". Since the cold cathode tube circuit has more impedance, the discharge of the delay line is somewhat slower resulting in a driving waveform having a slower rise time. This is advantageous because a fast rise time tends to cause ringing noise in the magnetic elements. To prevent this effect in the thyratron circuit a series resistor 33 may be placed in the discharge path of the delay line 28'. Furthermore, resistor 33 tends to make the discharge current more constant with changing of load impedance.

From the foregoing description, it is evident that Without the features provided by the present invention, gaseous tube driver circuits could not be used successfully in providing shifting pulses for magnetic shift register circuits. Accordingly, those novel features believed descriptive of the invention are defined with particularity in the appended claims.

I claim:

1. A circuit for energizing a plurality of static magnetic circuit elements, comprising in combination, a gaseous discharge device having a pair of input terminals and anode and cathode output electrodes, a power source connected for supplying discharge current for said device, an electromagnetic storage network coupled to said power source for assuming a charge of fixed value when said discharge device is not sustaining a discharge, means connected for selectively triggering the discharge device to cause discharge of said network through said device, and a load circuit coupling windings about said plurality of elements in series with the discharge current of said device.

2. A circuit as defined in claim 1 wherein the storage network, the load circuit and the discharge device anode are connected in series circuit in the order specified.

3. A circuit as defined in claim 1 wherein the storage network, the discharge device anode and cathode, and the load circuit are connected in series circuit in the order specified.

4. A circuit as defined in claim 3 wherein the elements of the load circuit are coupled in a circuit connected for generating a potential tending to trigger said discharge device, and means is provided for inhibiting the triggering potential generated in the load circuit at the input terminals of said discharge device.

5. A circuit as defined in claim 4 wherein the inhibiting circuit comprises a capacitive reactance network establishing both input terminals of said discharge device at substantially the same potential in response to said triggering potential generated in the load circuit.

6. A circuit as defined in claim 1 wherein the storage network, said discharge device and said load circuit are coupled in a series current branch adapted to receive discharge current from said network; and the storage network, the power source and the load circuit are coupled in a further series current branch adapted to receive charging current into said network, including a shunt current path around the load whereby switching of said elements in response to the charging current is prevented.

7. A circuit as defined in claim 6 wherein the load circuit path includes a series asymmetrical conductor in the current flow path.

8. A circuit as defined in claim 1 wherein the load circuit has a maximum impedance less than the charac teristic impedance of the delay line.

9. A circuit as defined in claim 1 wherein the charge and discharge paths of said network have separate current flow branches and said load circuit is in series with the current flow branch of only the discharge path.

10. A circuit as defined in claim 1 wherein the discharge device is a thyratron, whereby the triggering initiates discharge and thereafter for the duration of the discharge of said network has no control over the discharge.

11. A circuit as defined in claim 10 wherein the power source and storage network are coupled to the thyratron anode and the load is in the thyratron cathode circuit, whereby the delay line is essentially terminated by the load impedance during discharge of the thyratron, and low voltage insulation may be used in said windings.

12. A circuit as defined in claim 1 wherein the discharge device is a cold cathode gaseous tube, and the load circuit and tube impedance in series comprise the load impedance with which the delay line is terminated.

13. The combination in series circuit of a normally extinguished gaseous discharge device, an electromagnetic binary storage network, means for switching said storage network in one direction, a load circuit comprising at least one static magnetic inductor, and means to selectively trigger the gaseous discharge device into conduction to thereby switch said storage network in its other direction.

14. The combination define-d in claim 13 wherein the electromagnetic storage network is charged independently of the load circuit and is discharged through the discharge device and the load circuit.

15. The combination defined in claim l3 wherein the load circuit is in both the charge and discharge paths of the storage network, including a compensation network to prevent the inductors from changing magnetic state during charging of the network.

16. The combination defined in claim 13 wherin the load circuit is coupled between the input terminals of the discharge device, and an inhibiting network is provided for preventing triggering of the discharge device by spurious potentials developed within the load.

17. The combination defined in claim 16 wherein the input circuit comprises a grid and cathode, and the inhibiting network comprises a capacitive circuit maintaining the grid and cathode at the same A.-C. potential with respect to said spurious potentials.

18. The combination of a gaseous discharge device and a load circuit comprising at least one static binary magnetic storage element inductor in series circuit with said gaseous discharge device, means for switching said element in one direction, and means for producing a well defined current discharge pulse from said gaseous discharge device through said magnetic storage element in ductor to switch same in its other direction.

Browne Sept. 29, 1953 Booth June 8, 1954 

